Speed differential driving method and apparatus



March 21, 1967 J. D. BOADWAY SPEED DIFFERENTIAL DRIVING METHOD AND APPARATUS 2 Sheets-Sheet 1 Original Filed Feb. 26, 1962 INVIZN'IOR. day/v & 50404 4 March 1967 J. D. BOADWAY 3,309,781

SPEED DIFFERENTIAL DRIVING METHOD AND APPARATUS Original Filed Feb. 26, 1962 2 Sheets-Sheet 2 )RA 5Y5 A TT( United States Patent 3,369,781 SPEED DIFFERENTIAL DRIVING METHGD AND APPARATUS John I). Boadway, GrandMere, Quebec, Canada, assignor to Beloit Corporation, Beloit, Wis., a corporation of Wisconsin Continuation of application Ser. No. 175,574, Feb. 26, 1962. This application Dec. 9, 1964, Ser. No. 417,003 12 Claims. (Ci. 34-25) This is a continuation of my application Ser. No. 175,574 filed Feb. 26, 1962, previously copending herewith and now abandoned.

This invention relates to a method and apparatus for rotatably driving a plurality of cylindrical members to difierentially control the speeds of rotation thereof.

This invention also relates to a method of drying paper webs and to a drive mechanism for paper dryers.

It is known that if paper is allowed to shrink freely while drying, certain desirable properties are imparted to the paper.

A paper web, after wet pressing and as it enters the dry end of the paper machine, has a moisture content of approximately 65%. If the web is unrestrained as it dries to a moisture content of 45%, it will shrink very little. However, on drying from 45 to 9% moisture, the web may shrink as much as 12%.

The conventional system of gearing the dryers together, does not allow this shrinkage to take place, so that the web is under continually increasing tension as it dries. A sheet, which is allowed to shrink while drying will, after drying, exhibit stretchability or elongation before rupture of as much as 15%. On the other hand, the stretchability of a similar sheet dried under restriction and tension, may be as low as 2%.

It is Well recognized that a paper of substantial stretchability or extensibility possesses advantages For example, stretchability allows the paper to'withstand impact forces to a higher degree. It also permits papers, such as wrapping papers, to conform to the shape of the object which it carries, thus distributing the load and minimizing breakage. Therefore, there is an advantage in allowing the paper to shrink during at least a part of the drying procedure thereby to impart a high degree of stretchability to the paper.

The conventional drying procedures are not readily adaptable to accomplishments of this shrinking during drying. This is mainly due to the manner in which the drying cylinders are driven and the manner in which the paper is transported through the drying section of the paper machine. These conventional procedures are such that the paper web does not have the opportunity .to shrink but rather is continually subjected to a tension or draw which tends to adversely afiect the stress-strain characteristic of the paper.

It has heretofore been proposed to allow some shrinkage of the paper web to take place by using dryers of progressively smaller diameter. This has the difiiculty that the maintenance and replacement of the dryers is more difficult as they are no longer interchangeable and in the case of conversion from a system of equal diameter dryers to one of unequal diameters, the cost would be quite high. There is also a limitation in terms of variability as in the case where varying degrees of stretchability are required or in the case where a number of different grades of papers are being dried on a given machine.

It is a general object of this invention to provide a method and apparatus for rotatively driving a plurality of cylindrical members to differentially control the speeds of rotation thereof.

3,369,781 Patented Mar. 21, 1967 It is another object of this invention to provide a meth- 0d and means for carrying out the drying of a paper web whereby shrinkage thereof may be substantially accurately controlled and desirable characteristics thereby imparted to the web.

Mechanical drives, such as employed in paper machines, often involve the use of belts. One of the disadvantages of belt drives arises from the well known factor of belt slippage. This factor generally includes both the actual slippage or sliding of the belt on the pulley and the belt creep. However, in many instances where speeds are not excessive and proper attention is given to factors of belt and pulley friction, the main cause'of slippage is due to creep. The present invention seeks to take advantage of this belt creepage characteristic by employing it to effect desired control of relative speeds of various drying rolls.

The invention contemplates the use of a stretchable belt drive linking together a plurality of rotatably mounted elements or members. The tension change in the belt with power transmission from the belt to the moving member results in a change in they dimension of the belt and hence a change in its surface speed which in turn results in a change in the rotational speed of the member. Thus, by controlling this power of transmission to the belt, the power requirements of which can be Varied by an extraction of power from the system (by means of, for example, a generator), the belt can be made to. transmit minute differences in speed to the various rotating members of the system.

By way of explanation, it is of advantage to consider the details of a simple belt drive involving one driving pulley and one driven pulley. The driving pulley pulls on the belt creating a tension dilference so that the tension in the belt leaving the driving pulley is less than that as it goes on. If one considers the driven pulley as being pulled along by the belt, the tension is greater for that part of the belt leaving the pulley than that part going on. The tension difference across the driven p111 ley is equal and opposite to that of the driving pulley. As the belt passes over the driving pulley its tension is reduced and as it passes over the driven pulley its tension is increased.

Associated with the tension change across the pulleys,

there will be a dimension change due to the elastic prop ert-ies of the material. It is usual to keep this as low as possible in most belt materials. It will be apparent that the belt may be fabricated in such a way that definite known elastic properties are imparted to it.

If one considers the use of such an elastic belt for the above case of simple driving and driven pulleys, it

' can be seen that the belt, on the side which is tight will be longer and hence have higher surface speed than that on the other side, namely the slack side. Since the surface speed of the pulley will match the speed of the belt on the ingoing side of the pulley, a small difference in the a surface speed of the two pulleys will result. If the belt is truly elastic, this difference will-be directly proportional to the force being transmitted by the belt and can be computed from the knowledge of the elastic modulus.

The change in speed corresponding to the stretch of the belt represents a loss in power and efiiciency of power transfer. However, in spite of this, Where exact control of small speed differentials is needed it will be worthwhile losing this power to obtain the desired precision. For example, this is particularly useful where the belt is to be used to link a series of elements which carry a web of material (such as a paper Web) through a stage during which time the dimensions of the web themselves are changing.

There are two major methods of using a stretchable ,belt for speed differential control. For example, it may 3 drive a series of driven pulleys or it may link a series of driving pulleys.

The invention will be described with reference to the accompanying drawings, in which FIGURE 1 is a diagrammatic view of a driving system involving a series of driven pulleys;

FIGURE 2 is a schematic view of a driving system for paper machine dryers on a driven pulley basis; and

FIGURE 3 is a schematic view of an alternative driving system for paper machine dryers on a driving pulley basis.

Referring to FIGURE 1, pulleys 1, 2, 3, 4 and 5 are shown as linked together by an elastic belt 6. The pulley 1 is the driving pulley and the remaining pulleys are driven thereby through the belt. The tension of the belt is denoted by T subscript that pulley number onto which the belt must next go, i.e., T T T T T The power input at pulley 1 will give rise to a tension difference T T and the power taken out at any of the driven pulleys will give rise to a tension difference T -T at pulley 2, etc. Hence, the tension in the belt will increase as it goes over each driven pulley from 5 to 2, then decrease in passing over driving pulley 1. Due to the elastic property of the belt it will stretch and relax with changes in tension. Since the surface speed of both belt and pulley match as they meet, then the surface speed of each pulley from 1 to 5 will decrease with the decreasing tension in the belt as it passes over each pulley in turn.

The difference in speed between any two pulleys may be adjusted by adjustment of the power taken out at the pulley which first contacts the belt. For instance, if the power taken out at pulley 3 is increased while that at pulleys 2, 4 and 5 remains the same, then Tz-Tg increases. Sin-ce T is lowered and this controls the speed of pulley 3' it will decrease. Since T T and T -T are left unchanged because power taken out at pulleys 4 and 5 remains the same then pulleys 4 and 5 will also slow down but will keep the same relative speeds with respect to each other.

If the situation were reversed, i.e., if pulley 1 is the driven pulley and pulleys 2, 3, 4 and 5 are driving pulleys, the same effect is achieved except that the speed and tension differences will be in the opposite direction, i.e., T T T T T Thus, Whereas with driven pulleys, the speed increases in the direction of motion of the belt, with driving pulleys the speed decreases in the same direction. As with driven pulleys, a change in power transmission changes the relative speed between a given pulley and that pulley next contacting the belt.

For this relationship, a general equation may be written as follows:

where S=percent surface speed increase of that pulley following one being considered (in direction of belt in motion) P=horsepower being taken out at the pulley V=velocity of the belt ft./ minute E=elastic modulus of the belt in lbs.

Thus, if power is put in at the pulley, it becomes negative 'and so does S, signifying a decrease in surface speed.

Referring to FIGURE 2, a plurality of rotatably mounted paper machine dryer rolls or cylinders 7 are arranged in conventional manner to receive a paper web 8. The usual endless felt 9 is applied to each of the upper and lower series of dryer rolls, each such felt being carried by guide rolls 10, take-up rolls 11, spreader rolls 12, and idlers 13.

The dryer cylinders are driven by means of an endless elastic belt 14 which engages a pulley 15 mounted on each cylinder. The belt is driven by means of a driven pulley or roll 16. The belt is also supported on an idler roll 17, a guide roll 18, and take-up rolls 19 Since the paper is to be allowed to shrink, the later dryer cylinders must move slower than the first. Hence, if the speed differentials are to be achieved by means of the power taken out of the belt 14, the latter must contact the pulleys 15 in the opposite sequence to the movement of the paper web on the respective dryer cylinders. Thus, it is necessary to employ a pair of wrap rolls 20 in conjunction with each pulley 15. The belt has a predetermined modulus of elasticity which will permit control of individual speed differentials. Extra power beyond that required for rotation of the dryers is taken from the belt by any suitable means such as a brake or generator 21 on each of the dryers. It will be appreciated that, if a generator is employed as the power takeoff, the power generated can be fed back into the main D.C. power supply.

Referring to the alternative form of apparatus shown in FIGURE 3, each of the dryer cylinders 7 is driven by a motor 22 which supplies more than sufficient power to rotate it. The surplus power is taken up by the belt 14 through the pulleys 15 and absorbed by a generator 23 on the return travel. The speed of the generator 23 is controlled and the power absorbed is fed back into the system. In this case, the belt moves in the same direction as the paper web in order to obtain the speed differentials which will allow the web to shrink on drying.

In both systems illustrated, the dryers, which move at different surface speeds, run against the felt 9. Since this felt, which acts as a belt, moves in the direction of the paper web, it must shorten and reduce in tension. Thus, there must be a power transmission from dryers to felt and an absorption of this power in the return run of each felt is provided by means of a braking roll 24. It will be apparent that the characteristics of the felt must be such as to permit effective operation of the system described. In other words, the felt must be so designed that it imposes no interference upon the operation of the system as set forth. For instance, the felt will need to have a relatively very low elastic modulus whereby it will absorb insufficient power to interfere with the draw control.

It will be understood that the belt 14 will be so mounted and arranged that no sliding of the belt on the pulleys will occur, and to this end is equipped with the conventional idler rolls 17, guide rolls 18 and take-up rolls 19. On the other hand, creep, which is the basis for achieving speed control in accordance with the invention, must occur.

While the invention has been described with reference to speed differentials between individual dryer cylinders,

it will be apparent that it may also be applied to the control speed differentials between groups or series of dryers.

It may be desirable in some instances to have percentage changes in surface speeds which are in excess of that allowable by the elastic properties of one main endless belt. This problem may be overcome when driving multiple rotating units, by linking together as many rotating units as can be readily accommodated by the elastic properties of one endless belt, then repeating this for an additional section of rotating units until all units are belt driven; the sections themselves may be readily linked together by making one rotating unit common to each pair of endless belts on adjoining sections.

It will be apparent that various modifications of the invention may be made within the broad concept thereof. Moreover, it will be understood that any required modification of associated elements may be carried out whenever necessary. For instance, the dryer cylinder surface may require known treatment to reduce adhesion thereto of the paper web as it is pressed against the same by the felt. For example, also, the felt may be so formed and its guide rolls may be so arranged, braked or powered to give it characteristics which will not adversely interfere with the desired aim of imparting stretchability to the paper web.

I claim as my invention:

1. In combination with a plurality of rotatably mounted cylindrical members, a system for dilferentially controlling the speed of rotation of said members which comprises a pulley fixed in axial relation to each of said members, an endless belt having a predetermined modulus of elasticity drivably engaging all of said pulleys, at least one additional rotatably mounted pulley drivably engaging said belt, at least one of said pulleys being driven to impart travelling movement to said belt and rotation to said pulleys and cylindrical members, and means resisting rotation of at least one of said pulleys to extract at least a portion of the rotative power applied thereto by said belt.

2. In combination with a plurality of rotatably mounted cylindrical members, a system for differentially controlling the speed of rotation of said members which comprises a pulley fixed in axial relation to each of said members, an endless belt having a predetermined modulus of elasticity drivably engaging all of said pulleys, a rotatably mounted driven pulley drivably engaging said belt to impart travelling movement thereto and rotative movement to said pulleys and cylindrical members, and separate power takeofi means associated with each of said cylindrical member pulleys to extract therefrom power in excess of that required for rotation thereof.

3. In combination with a plurality of rotatably mounted cylindrical members, a system for difierentially controlling the speed of said members which comprises a pulley fixed in axial relation to each of said members, an endless belt having a predetermined modulus of elasticity drivably engaging all of said pulleys, separate power means driving each of said pulleys to cause rotative movement thereof and to impart travelling movement to said belt, and power extraction means engaging said belt to extract at least a portion of the travelling power applied thereto.

4. In combination with a plurality of rotatably mounted paper machine drying cylinders, a system for differentially controlling the speed of rotation of said cylinders which comprises a pulley fixed in axial relation to each of said cylinders, an endless belt having a predetermined modulus of elasticity drivably engaging all of said pulleys, a driven roll drivably engaging said belt to impart travelling movement thereto and rotative movement to said cylinders, take-up and guide rolls supporting said belt for non-slip engagement with said pulleys, and power extraction means associated with each of said pulleys for independent, selective extraction of excess rotative power applied to said pulleys by said belt.

5. In combination with a plurality of rotatably mounted paper machine drying cylinders, a system for differentially controlling the speed of rotation of said cylinders which comprises a pulley fixed in axial relation to each of said cylinders, an endless belt having a predetermined modulus of elasticity in driving engagement with all of said pulleys, power means independently driving each of said pulleys and cylinders and imparting travelling movement to said belt, and power extraction means engaging said belt to extract at least a portion of the travelling power imparted thereto.

6. A system as defined in claim 4 including an endless felt extending about a portion of the circumference of each said cylinder, said felt having a direction of travelling movement substantially reverse to that of said belt, said felt having characteristics ineffective to modify said power extraction means.

7. A system as defined in claim 5, including an endless felt extending about a portion of the circumference of each said cylinder, said felt having characteristics ineffective to modify said power extraction means.

8. A method of rotatably driving a plurality of cylindrical members to differentially control the speeds of rotation thereof which comprises elastically connecting all of said members together to provide a closed driving system for transmission of rotative driving power from one to another of said members, applying a driving force to said system at at least one point therein, and extracting power in a controlled amount at a difierent point therein to obtain a predetermined speed relationship between different members.

9. A method of rotatively driving a plurality of cylindrical members to differentially control the speeds of rotation thereof which comprises elastically connecting all of said members together to provide a closed driving system for transmission of rotative driving power from one to another of said members, applying a driving force to said system at at least one point therein, and selectively extracting power from the rotative driving power applied to each of said members.

10. A method of rotatively driving a plurality of cylindrical members to differentially control the speeds of rotation thereof which comprises elastically connecting all of said members together to provide a closed driving system for transmission of rotative driving power from one to another of said members, applying a driving rotative force to each of said members, and extracting power from said system at one point therein, independently of said system.

11. A method of drying a paper web which comprises directing said web over a successively arranged series of drying cylinders, elastically connecting said cylinders to provide a closed rotative driving system for transmission of rotative power from one to another of said cylinders, applying rotative driving power at at least one point in said system at a point between said cylinders, and extracting power from said system to differentially control the speed of rotation of each said cylinder and thereby control the shrinkage of said paper web.

12. In combination with a plurality of rotatably mounted cylindrical members, a system for differentially controlling the speed of rotation of said members which comprises a pulley fixed in axial relation to each of said members, said members being arranged in a plurality of series, one said member of each said series being common -to another of said series, an endless belt having a pre- References Cited by the Examiner UNITED STATES PATENTS 7/1933 Vedder 34ll6 9/1934 Bleibler 34-113 X FREDERICK L. MATTESON, JR., Primary Examiner.

WILLIAM F. ODEA, JAMES W. WESTHAVER,

Examiners. C. R. REMKE, Assistant Examiner. 

9. A METHOD OF ROTATIVELY DRIVING A PLURALITY OF CYLINDRICAL MEMBERS TO DIFFERENTIALLY CONTROL THE SPEEDS OF ROTATION THEREOF WHICH COMPRISES ELASTICALLY CONNECTING ALL OF SAID MEMBERS TOGETHER TO PROVIDE A CLOSED DRIVING SYSTEM FOR TRANSMISSION OF ROTATIVE DURING POWER FROM ONE TO ANOTHER OF SAID MEMBERS, APPLYING A DRIVING FORCE TO SAID SYSTEM AT AT LEAST ONE POINT THEREIN, AND SELECTIVELY EXTRACTING POWER FROM THE ROTATIVE DRIVING POWER APPLIED TO EACH OF SAID MEMBERS. 